Acoustic sensing device

ABSTRACT

A sensing device having a high frequency sonic wave source that generates an acoustic beam is supplied by a fluid source at above ambient pressure serially connected through a normally open fluidic switch connected in the circuit as an OR gate. The sonic wave generator is disposed to direct an acoustic beam toward a target where it is reflected towards the control input of an acoustically sensitive fluidic receiver whose output is connected to the control input of the fluidic switch. The latter is modulated by the output of the receiver which is responsive to the acoustic beam in such a way that the fluidic switch is changed to a flow inhibiting condition by the receiver when the reflected acoustic beam is present and to a flow passing condition by the receiver when the reflected acoustic beam is absent. The sonic wave generator is thereby maintained in an oscillatory mode in an on-off sequence such as an equal wave multivibrator. The period of the multivibrator in the sensing device is dependent on two factors: (1) the time constant of the fluidic circuit and (2) the time of propagation of the sound from the generator to the acoustically sensitive fluidic receiver. The former is a constant which can be determined for each circuit and the latter is dependent on variable conditions external to the fluidic circuit. This permits measurement of dependent variable conditions of the system, through which the acoustic beam passes, viz. distance that the acoustic beam travels as well as temperature, density and composition of the fluid medium through which the acoustic beam travels.

iJite tates i [1 1 eeen et al.

[ ACOUSTIC SENSING DEVICE [75] Inventors: Basil B. Beeken, New Haven;Robert F. OKeefe, Trumbell, both UNITED STATES PATENTS 3,178,677 4/1965Hadley et al.. ..340/l R 2,400,309 5/1946 Kock ....340/3 E 3,412,37011/1968 Massal ....340/l R 3,491,332 1/1970 Lomas et al. ..340/1 R3,500,952 3/1970 Beeken ..181/0.5 NP 2,511,599 6/1950 Rochester....340/3 E 3,500,951 3/1970 Beeken ..l8 l/0.5 NP

Primary Examiner-Richard A. Farley Attorney-Alan H. Levine I [57]ABSTRACT A sensing device having a high frequency sonic wave 51 Apr. 24,1973 source that generates an acoustic beam is supplied by a fluidsource at above ambient pressure serially connected through a normallyopen fluidic switch connected in the circuit as an OR gate. The sonicwave generator is disposed to direct an acoustic beam toward a targetwhere it is reflected towards the control input of an acousticallysensitive fluidic receiver whose output is connected to the controlinput of the fluidic switch. The latter is modulated by the output ofthe receiver which is responsive to the acoustic beam in such a way thatthe fluidic switch is changed to a flow inhibiting condition by thereceiver when the reflected acoustic beam is present and to a flowpassing condition by the receiver when the reflected acoustic beam isabsent. The sonic wave generator is thereby maintained in an oscillatorymode in an on-off sequence such as an equal wave multivibrator. Theperiod of the multivibrator in the sensing device is dependent on twofactors: (1) the time constant of the fluidic circuit and (2) the timeof propagation of the sound from the generator to the acousticallysensitive fluidic receiver. The former is a constant which can bedetermined for each circuit and the latter is dependent on variableconditions external to the fluidic circuit. This permits measurement ofdependent variable conditions of the system, through which the acousticbeam passes, viz. distance that the acoustic beam travels as well astemperature, density and composition of the fluid medium through whichthe acoustic beam travels.

4 Claims, 4 Drawing Figures AIR SUDDLY Patented April 24, 1973 2Sheets-Sheet 1 FIGJ FIG.2

mvem'ons ROBERT F. O'KEEFE BASIL B. BEEKEN W ha ATTORNEY Patented April24, 1-973 2 Sheets-Sheet 2 ACOUSTIC (A) BEAM 0 Z Q UW HO II T I LL L MTU W GD. T MN TN WE T T lN W CHAN UWAHVLM.

5 CC 06 FI m m w m m m wwwuwu I NVENTORS l2 I4 '6 I8 20 22 24 26 28 3032 3 ROBERT F DISPLACEMENT BASIL B. BEEKEN M flu/64 ATTORNEY ACOUSTICSENSING DEVICE BACKGROUND OF THE INVENTION This invention relates to anovel acoustic sensing system and more particularly to an acousticsensing system which can be adapted to measure variable parameters in ahostile or explosive environment.

avoid this maintenance problem as well as to conserve on spacerequirements, electrical components have been substituted for use inhostile and explosive environments. However these too are bulky sincethey require explosion proof cases to prevent any possibility of a sparkor current surge initiating an explosion. Further, it is not alwayspossible to keep power requirements below danger levels with electricalcomponents since the production of intelligible signals at a distanceoutside of the environment being measured, requires a minimum amount ofpower.

Thus it is quite clear that because of the size and the requisite movingparts of conventional fluid type sensing devices, their use has beenlimited especially where it would appear thatthey would offer the mostutility.

There is a present need for fluidic devices which contain no movingparts for use in many areas of various technologies, for example, in themeasurement of temperature, densityor composition of a sealed hostilefluid environment or where the level of an explosive fluid in a storagecontainer must be periodically determined without subjecting man to thehostile conditions and without using mechanical or electrical energywhich could trigger an explosion. Thus in these applications where sizeand movement of parts are of overriding importance because of theenvironment in which the device is to be used or because oftheapplication to I which the device is to be. put, there is a'need for afluidic device which is, substantially maintenance free,

and safe to'use in explosive environadapted to the measurement ofvariable parameters of interest, especially adaptable to hostile orexplosive environments.

BRIEF SUMMARY OF THE INVENTION The present invention obviates theforegoing disadvantages of prior art fluid type sensing devices byproviding a unit which is compact, safe in an explosive environment andwhich does not incorporate moving parts for theoperation thereof. Theunit is thus capable of operating in hostile and explosive environmentsto measure parameters'of interest therein upon demand from personnel whodo not have to be subjected to the contaminants or dangers of theenvironment and who can thus work safely at a distance from themeasuring equipment.

In accordance therewith, the present invention provides for anacousticsensing system which comprises an acoustic wave generating means forpropagating an acoustic wave, an acoustic wave receiving meanspositioned so as to be capable of receiving the acoustic wave anddeveloping a perceptible output in response thereto, and a switchingmeans for variably controlling the acoustic wave generating means tomodulate the acoustic wave propagated thereby in response to theperceptible output of the acoustic wave receiving means.

Having briefly described an embodiment of the present invention, it is aprinciple object thereof to provide a new and improved acousticalsensing device.

It is another object of the present invention to provide a fluid typesensing device having no moving parts.

It is further object of the present invention to provide a fluid typesensing device which includes feedback loop means for gating the outputof an acoustical wave generating means.

It is a still further object of the present invention to provide a fluidtype sensing device which includes control means operationally connectedto respond to the acoustic wave receiving means and to control theoutput of the acoustical wave generating means in a multivibrator mode.

It is an added object of the present invention to provide a fluid typesensing device which includes means for gating the acoustical wavegenerating means or source supply in accordance with a gating frequencywhich corresponds to the value of the variable parameter of interest.

It is an additional object of the present invention to provide a fluidtype sensing device which includes means for adapting the instant gatingfrequency at which the acoustical wave generating means supply isoperated in accordance with the sensed value of the variable parameterof interest.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be morereadily apparent from an understanding of the following detaileddescription of one embodiment of the present invention when consideredin conjunction with the accompanying drawings in which like referencenumerals refer to like elements in the various figures and in which:

FIG. 1 illustrates in block form a network for a fluid type sensingdevice embodying the present invention;

FIG. 2 illustrates in schematic form a network for a fluid type sensingdevice conforming to the block diagram shown in FIG. 1;

FIGS. 3A to 3H are timing diagrams for the signal responsive networkshown in FIGS. 1 and 2; and

FIG. 4 illustrates a graph of displacement of an object of interest fromthe inventive fluid type sensing device plotted against frequency of thepulses modulating the acoustical wave generating means whichdemonstrates the accuracy of the device.

DESCRIPTION OF THE PREFERRED EMBODIMENT An acoustic sensing system isshown generally at 2 in FIG. 1, and includes an acoustic wave generatingmeans 4, an acoustic wave receiving means 6, and a switching means 8. Asource of power or fluid pressure 10 is provided to supply the acousticwave receiving means 6 and the acoustic wave generating means 4 throughthe switching means 8 with, for example, air under pressure. The outputof the acoustic wave receiving means 6 is delivered to the switchingmeans 8 and the system frequency is measured at terminal 12 which isconnected to an output of the switching means 8.

An acoustic wave is illustrated at 14 being generated from the acousticwave generating means 4 and directed toward a surface 16 capable ofreflecting the acoustic wave. The wavefront of the acoustic wave 14striking the surface 16 is reflected at an equal and opposite angle, asis well known, forming a reflected acoustic wave 18 which is received atan ear 20 of the exponential horn type of the acoustic wave receivingmeans 6, the output of which is in phase with its input. The switchingmeans 8 is such that power is passed therethrough from the source ofpower to the input of the acoustic wave generating means 4 while thereis no signal present from the output of the acoustic wave receivingmeans 6 and power to the acoustic wave generating means 4 is interruptedwhen there is a measurable signal received from the output of theacoustic wave generating means 6.

Thus when the reflected acoustic wave 18 is received at the ear 20, ameasureable signal is generated which when received at the switchingmeans 8, interrupts the power supplied to the acoustic wave generatingmeans 4 and the acoustic wave 14 is no longer generated. This absence ofan acoustic wave 14 at the car changes the potential of the generatedsignal at the output of the acoustic wave receiving means 6 to its lowervalue which again changes the mode of operation of the switching means 8to allow power to pass therethrough to the acoustic wave generatingmeans 4.

It can be seen that the period of the generated signal at the output ofthe acoustic wave receiving means 6 is proportional to the time that ittakes the acoustic wave 14 and the reflected acoustic wave 18 to travelfrom the acoustic wave generating means 4 to the car 20. Thus thefrequency of the generated signal is a measure of the distance betweenthe acoustical sensing system 2 and a surface 16 or if the distance isknown a measure of the physical properties of the medium through whichthe acoustic wave 14 travels as will be shown below.

In FIG. 2, a whistle 30 is used as a specific embodiment of the acousticwave generating means 4 of FIG. 1. The whistle 30 is described in U.S.Pat. No. 3,432,803 issued to 13.8. Beeken on Mar. 11, 1969. Likewise, asensing unit 32 is used as a specific embodiment of the acoustic wavereceiving means 6 of FIG. 1. The sensing unit 32 is described in U.S.Pat. No. 3,500,952 issued to BB. Beeken on Dec. 20, 1967. Finally, for aspecific embodiment of the switching means 8 of FIG. 1 there is shown afluid amplifier 34 which is described in U.S. Pat. No. 3,507,295 againissued to BB. Beeken on Apr. 2|, I970.

The individual portions of the acoustical sensing device having beendescribed by reference to published U .S. Patents, the operation of thedevice will be explained in greater detail with reference to FIG. 2.

It should be noted that the sensing unit 32 in the unit describedherein, consists of two flow mode devices or two cascaded amplifierstages viz. a first low powered stage of amplification and a secondhigher power stage. The fluid amplifier 34 for example, a switchingmeans for supplying fluid pressure to a fluid inlet also consists of twocascaded stages of amplification of a wall attachment device.

A fluid pressure source or supply 36 provides air under pressure to themain supply channel 38 and to the supply channel 39 of fluid amplifier34 and to the fluid supply inlet groove 40 of the sensing unit 32. Letit be assumed that the amount of pressure in collector 42 and thus inthe output 44 of the sensing unit 32 is initially in the lower mode.Then the fluid from the fluid pressure supply 36 passes through the mainsupply channel and supply channels 38 and 39, respectively, to collectoroutput channel or outlet channel 46, through feed line 48 and into fluidsupply inlet or fluid inlet 50 of the whistle 30. With fluid underpressure being received at the fluid inlet 50, the whistle 30 propagatesa sonic or acoustic wave 14 of for example, 50 kilocycles per second outof cavity 52 which wave front is reflected off of surface 16 and formsreflected acoustic wave 18 which is received at a signal input or soundwave receiving opening 54 in sensing unit 32 which is a wave receivingmeans such as for example, a flow mode type amplifier. The signal inputcan include an exponential horn (as shown) which is well known, forgreater sensitivity. Although acoustic wave 14 is shown exiting fromcavity 52 at an acute angle, it should be understood that the axis ofcavity 52 is substantially in line with acoustic wave 14.

Sensing unit 32 is a two stage fluidic amplifier arranged to produce asignal at the output 44 which is in phase with the envelope of the inputsignal received at sound wave receiving opening 54. Thus, with apositive pressure being received (viz. the presence of the envelope ofthe acoustic wave 18 at the source wave receiving opening 54) the highermode or level of pressure is present at the output 44 and at controlchannel 56 through connecting line 58 which connects the former to thelatter.

This higher pressure at control channel 56 interrupts the higherpressure fluid passing through main supply channel 39 to outlet channel46, feed line 48 and fluid inlet 50, so that the whistle stopsgenerating an acoustic wave 14. With the absence of the acoustic wave14, there is in time, no longer a reflected acoustic wave present at thesecond wave receiving opening 54 and the output 44 being in phasetherewith produces a lower pressure mode signal thereby changing thesignal value at control channel 56 to the lower potential andeffectively changing the flow operation of the fluid amplifier 34, toallow the air from the fluid pressure source 36 to pass to the'fluidinlet 50 through the feed line 48 and thereby to initiate the whistle 30to generate an acoustic wave 14.

Thus the fluid amplifier 34 and the sensing unit 32 are operated asmonostable multivibrators and the signals produced at output 44 and atoutlet channel 46 are square wave forms whose period is equal to thetime lapse measured between the initiation of two successive acousticwaves 14.

A frequency meter 60 can be connected to outlet channel 62, for example,to display the frequency of the square wave. Alternately or incombination, as desired, the square wave can be used to initiateoperations of equipment dependent on the parameters being measured, asis will known in the art.

The operations of this acoustic sensing system 2 is best understood withreference to various combinations of potentials which may be applied tothe inputs.

Graphic illustrations of the signals applied to sound wave receivingopening 54, control channel 56 and fluid inlet 50 and of the signalsreceived at output 44, outlet channel 46 and cavity 52 are shown inFIGS. 3A through 3F inclusive, but not necessarily in the ordermentioned.

In FIG. 3A, at time t an acoustic wave 14 of+ magnitude is beinginitiated from cavity 52. At time t the wave front of the reflectedacoustic wave reaches the sound wave receiving opening 54 (FIG. 3B) andthe pressure increases from to at FIG. 38 under an envelope for example,of a 50 kc per second wave. Approximately 1 millisecond later at time t,(the response time averaged out for a fluidic sensing unit) the pressureat output 44 as shown in FIG. 3C and likewise the control channel 56 asshown in FIG. 3D rises from O to (the flow time in the connecting line58 being considered negligible). At approximately I millisecond later,(the response time of the fluid amplifier 34) time I the pressure atoutlet channel 46 (shown in FIG. 3B) drops from a pressure of which itmaintained from before t to a pressure of 0. Simultaneously (because ofnegligible line loss time) the pressure at fluid inlet 50 (FIG. 3F)drops from to 0. At time t. (which is 1 millisecond later than becauseof the whistle 30 response time) the generation of acoustic beam 14 atcavity 52 is abruptly stopped (FIG. 3A) and the pressure drops from to0.

This signals the end of the first half cycle of operation. At time [theperiods (t t and (t being the time it takes for the acoustic wave 14 totravel from the cavity 52 toward the surface 16 and back as reflectedacoustic wave 18 into the sound wave receiving opening 54], the pressurewave enveloping the 50 kilocycle per second signal drops from to 0 atsound wavereceiving opening 54 (FIG. 33). At the output 44 (FIG. 3C) andthe control channel 56 (FIG. 3D) drops from a pressure of -lto 0. Then Imillisecond later at time 1, outlet channel 46 (FIG. 3B) increases froma 0 to a pressure and simultaneously fluid inlet 50 (FIG. 3F) increasesfrom 0 to pressure.

At 1 millisecond later, time i the acoustical beam is again generatedfrom cavity 52 (FIG. 3A). This is the second half cycle and it isrepeated, as the acoustic wave is repeatedly initiated and extinguished.

The use of the acoustic sensing system can be seen from an analysis ofthe timing diagram. The time period (FIG. 36) represented by (t t and (t2 is the time it takes for the acoustic wave 14 to travel through theenvironment, and be reflected back to the sound wave receiving opening54 and will be referred to as T The time period (FIG. 3H) represented by(1 t and (n t is the time it takes for the closed loop to initiate aresponsive change in the cavity 52 and will be referred to as T,,".Therefore the total time T for one full cycle of operation, i.e., thetime between the initiation of two successive acoustic waves 14 is:

Tr= 2 w TL) and the frequencyf, of the square wave is:

where T 2/0 x/cos 9 where x is the distance from the cavity 42 to thereflecting surface 16 and c is the speed of propagation of sound, whichis a known constant at known temperatures and environment conditions.However, because of the close relative spacing of the cavity 52 and thesound wave receiving opening 54 compared to the distance from thesurface 16, the angle 0 (FIGS. 1 and 2) is nearly 0 and therefore thecos 0 is nearly 1. Therefore or since T and c are known if solved for x:

And therefore the distance x, can be obtained from a knowledge of thefrequency of the circuit, with c a known variable and T fixed for eachcircuit. Where x is a known constant, the temperature, density orcomposition of a fluid environment through which the acoustic beam 14travels which are all well known functions of 0, can be obtained. Therelationships of these parameters are well known and one skilled in theart can easily use one or more acoustic sensing systems to measuretemperature or compositions or density on the basis of the instantdisclosure.

An example of measurements ofx made with an embodiment of the acousticsensing device is shown in FIG. 4 which is a graph of displacement of anacoustic reflecting surface from the inventive embodiment of theacoustic sensing device plotted against the frequency measured for eachdisplacement. Both the theoretical curve T and the actual curve A areshown for comparison.

Each measurement was made over a 10 second count interval so that theresolution of the measurements are approximately one-fourth inch asshown by the band marks at each plotted point. It can be seen from FIG.4 that the theoretical line T asymptotically approaches the actual curveA as the displacement is increased. This can be attributed to the cos 0function which was considered negligible during measurements, since theangle 0 more closely approaches 0 as the displacement increases.

Although not completely understood, it is proposed that the onlytheoretical requirements for a device to operate as describedhereinabove is that a sonic generator be controlled as to its output inaccordance with a positive feedback of the energy output which feedbackis a function of an energy wave reflecting substantially all of theenergy back to the feedback circuit. Because of the nearly percentpositive feedback the feedback circuit is operated as a relaxationoscillator so that the oscillators are in two distinct regions ofoperation producing a square wave control of the sonic generator.

It is thus apparent from the foregoing that there has been provided anacoustic sensing device which achieves the foregoing objects andadvantages of the present invention. The acoustic wave receiving meanscan be a two stage fluidic amplifier as shown or any amplifier which hasits output in phase with its input or out of phase with its input byadjusting the switching means accordingly. The acoustic wave is thusamplitude modulated between an on state and an off state whereby theacoustic wave generating means produces an output which includes acarrier wave and the output is larger than the carrier wave during theon state and the output is equal to the carrier wave during the ofstate. The carrier wave is preferentially of a substantially potential.As an example, the switching means can be relaxation type, specificallya monostable multivibrator as shown, and its output should be such thatpower is delivered to the acoustic wave generating means in response tono reflected wave being present at the acoustic wave receiving means andvice versa. It is to be understood that the invention is not to beconsidered as limited to the specific embodiment described above andshown in the accompanying drawings, which embodiment is merelyillustrative of the best mode presently preferred for carrying out theinvention and is susceptible to change in form, size, detail andarrangement of components, but rather the invention is intended to coverall such variations, modifications, and equivalents thereof as may bedeemed to be within the scope of the claims depended hereto.

We claim: 1. An acoustic sensing system comprising: a. a whistle forpropagating a sonic wave in a medium, said whistle having a fluid supplyinlet b. wave receiving means including a flow mode type amplifierhaving a signal input channel, an emitter channel and a collector outputchannel, said emitter channel being connected to a supply of fluid underpressure so as to cause a jet of fluid to be issued from said emitterchannel towards said collector, output channel, said signal inputchannel being adapted to receive said sonic wave and direct the sameagainst said jet of fluid so as to thereby switch the mode of operationof said amplifier and thus vary the output pressure in said collectoroutput channel c. a fluidic amplifier for supplying fluid pressure tosaid fluid inlet of said whistle under the control'of said fluid outputpressure in said collector output channel of said flow mode typeamplifier; said fluidic amplifier having a supply channel connected tothe supply of fluid under pressure, a control channel connected to theoutput channel of the flow mode type amplifier, and a collector channelconnected to the fluid supply inlet of the whistle; said fluidicamplifier being operatively connected to change the amount of fluidpressure applied to said inlet of said whistle from a first level to asecond level when said fluid output pressure from the collector outputchannel of the flow mode type amplifier is indicative of said sonic wavebeing present at said signal input channel and to reverse the amount offluid pressure applied to said whistle fluid inlet to said first levelwhen said sonic wave is absent at said signal input channel, saidwhistle producing said sonic wave only when the fluid pressure appliedto its inlet is at said first level, whereby said sonic wave isintermittently automatically enerated by said whistle in a periodicmanner sucE that the wave period is a function of inter alia thedistance that said sonic wave travels through said propagating medium.

2. Apparatus as defined by claim 1, wherein said whistle includes acavity, and said cavity and said signal input channel are mutuallyspaced from the surface of a sound reflecting medium to be sensedwhereby said sonic wave propagated through said medium by said whistleis reflected at said surface toward said signal input channel.

3. Apparatus as defined by claim 2, wherein said flow mode typeamplifier includes a first and second stage amplifier, said first stageamplifier having a first stage collector channel, said emitter groovechannel and said signal input channel and said second stage amplifierhaving said collector channel, a second stage emitter groove channel anda second stage signal input channel, said first stage collector channelbeing operatively connected to said second stage signal input channel sothat said signal appearing at said first stage collector channel isamplified thereby.

4. Apparatus as defined by claim 3, wherein said emitter groove of saidfirst stage amplifier includes an exponential ear having its outputconnected to said emitter groove and its input at the opposite endthereof and the axis of said exponential ear being substantiallyparallel to the axis of said cavity of said whistle.

1. An acoustic sensing system comprising: a. a whistle for propagating asonic wave in a medium, said whistle having a fluid supply inlet b. wavereceiving means including a flow mode type amplifier having a signalinput channel, an emitter channel and a collector output channel, saidemitter channel being connected to a supply of fluid under pressure soas to cause a jet of fluid to be issued from said emitter channeltowards said collector, oUtput channel, said signal input channel beingadapted to receive said sonic wave and direct the same against said jetof fluid so as to thereby switch the mode of operation of said amplifierand thus vary the output pressure in said collector output channel c. afluidic amplifier for supplying fluid pressure to said fluid inlet ofsaid whistle under the control of said fluid output pressure in saidcollector output channel of said flow mode type amplifier; said fluidicamplifier having a supply channel connected to the supply of fluid underpressure, a control channel connected to the output channel of the flowmode type amplifier, and a collector channel connected to the fluidsupply inlet of the whistle; said fluidic amplifier being operativelyconnected to change the amount of fluid pressure applied to said inletof said whistle from a first level to a second level when said fluidoutput pressure from the collector output channel of the flow mode typeamplifier is indicative of said sonic wave being present at said signalinput channel and to reverse the amount of fluid pressure applied tosaid whistle fluid inlet to said first level when said sonic wave isabsent at said signal input channel, said whistle producing said sonicwave only when the fluid pressure applied to its inlet is at said firstlevel, whereby said sonic wave is intermittently automatically generatedby said whistle in a periodic manner such that the wave period is afunction of inter alia the distance that said sonic wave travels throughsaid propagating medium.
 2. Apparatus as defined by claim 1, whereinsaid whistle includes a cavity, and said cavity and said signal inputchannel are mutually spaced from the surface of a sound reflectingmedium to be sensed whereby said sonic wave propagated through saidmedium by said whistle is reflected at said surface toward said singalinput channel.
 3. Apparatus as defined by claim 2, wherein said flowmode type amplifier includes a first and second stage amplifier, saidfirst stage amplifier having a first stage collector channel, saidemitter groove channel and said signal input channel and said secondstage amplifier having said collector channel, a second stage emittergroove channel and a second stage signal input channel, said first stagecollector channel being operatively connected to said second stagesignal input channel so that said signal appearing at said first stagecollector channel is amplified thereby.
 4. Apparatus as defined by claim3, wherein said emitter groove of said first stage amplifier includes anexponential ear having its output connected to said emitter groove andits input at the opposite end thereof and the axis of said exponentialear being substantially parallel to the axis of said cavity of saidwhistle.